<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        html, body {
            padding: 0;
            margin: 0;
        }

        .box {
            position: fixed;
            left: 50%;
            top: 50%;
            transform: translate(-50%, -50%);
            width: 630px;
            height: 630px;
            background-color: red;
        }
    </style>
</head>
<body>
<div class="box"></div>
</body>
</html>